Thursday, October 28, 2010

Connect the Spots: Revealing Leopard Seal Secrets

Despite such insights, there is very little data on leopard seal behavior. Questions abound regarding the species's population dynamics and breeding habits. Scientists like Rogers still do not know whether leopard seals stay in the areas where they were born, if either sex establishes new territories, how long pups stay with their mothers, or why juveniles roam as far north as Australia.

Even the total population size is under debate. Rogers suspects that many males may be missed during visual surveys conducted during breeding season because males are underwater calling to and listening for females. Seeking a more accurate estimate, Rogers has deployed sonar buoys beneath the ice to record and count vocalizations.

Male and female vocalization patterns themselves are of great interest to Rogers and her colleagues, in particular because leopard seals are such solitary creatures. To find one another they must communicate clearly over large distances. Their songs, therefore, must be highly structured, Rogers noted, and can be ornamented with distinctive trills reminiscent of bird or cricket calls.

Female leopard seals have been found to sing as well as males during breeding season, a notable exception in the animal world. Such a skill is necessary, given that each solitary female reaches her three- to four-day receptive phase independently, a phenomenon known as asynchronous estrus. If females were unable to convey this important mating and location information, males would not know which females were receptive or where to find them.

Yet little is known about what happens when males and females meet, Rogers said. Adult females are noticeably larger than males, growing up to 3.6 meters (12 feet) long and weighing up to 450 kilograms (990 pounds). So, Rogers wonders, do the larger females select their mates if more than one male answers their call?

Another curious aspect to leopard seal vocalizations is their use of high-pitched clicks up to 165 kilohertz, a frequency far beyond the range of normal human hearing. Rogers speculates leopard seals might use these clicks to echolocate food and air holes during dark, ice-bound winters.

With "a myriad of questions" still to be answered, Rogers hopes future use of instruments such as Crittercam (see sidebar) might reveal more detailed information on the species's feeding patterns, hunting techniques, and mating behaviors. Such information will be crucial to a better understanding of these mysterious creatures and the fragile Antarctic habitat they call home.